[Intel-gfx] [PATCH] drm/i915/backlight: Fix backlight takeover on LPT

[Maarten Lankhorst]

On lynxpoint the bios sometimes sets up the backlight using the CPU
display, but the driver expects using the PWM PCH override register.

Read the value from the CPU register, then convert it to the other
units by converting from the old duty cycle, to freq, to the new units.

This value is then programmed in the override register, after which
we set the override and disable the CPU display control. This allows
us to switch the source without flickering, and make the backlight
controls work in the driver.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=108225
Cc: Basil Eric Rabi <ericbasil.rabi at gmail.com>
Cc: Hans de Goede <jwrdegoede at fedoraproject.org>
Cc: Tolga Cakir <cevelnet at gmail.com>
Tested-by: Tolga Cakir <cevelnet at gmail.com>
---
 drivers/gpu/drm/i915/intel_panel.c | 34 +++++++++++++++++++++++++++---
 1 file changed, 31 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c
index e6cd7b55c018..3357232f1b0e 100644
--- a/drivers/gpu/drm/i915/intel_panel.c
+++ b/drivers/gpu/drm/i915/intel_panel.c
@@ -1485,7 +1485,7 @@ static int lpt_setup_backlight(struct intel_connector *connector, enum pipe unus
 	struct drm_i915_private *dev_priv = to_i915(connector->base.dev);
 	struct intel_panel *panel = &connector->panel;
 	u32 pch_ctl1, pch_ctl2, val;
-	bool alt;
+	bool alt, cpu_mode = false;
 
 	if (HAS_PCH_LPT(dev_priv))
 		alt = I915_READ(SOUTH_CHICKEN2) & LPT_PWM_GRANULARITY;
@@ -1507,12 +1507,40 @@ static int lpt_setup_backlight(struct intel_connector *connector, enum pipe unus
 
 	panel->backlight.min = get_backlight_min_vbt(connector);
 
-	val = lpt_get_backlight(connector);
+	panel->backlight.enabled = pch_ctl1 & BLM_PCH_PWM_ENABLE;
+	if (panel->backlight.enabled && HAS_PCH_LPT(dev_priv) &&
+	    (I915_READ(BLC_PWM_CPU_CTL2) & BLM_PWM_ENABLE) &&
+	    !WARN_ON(pch_ctl1 & BLM_PCH_OVERRIDE_ENABLE)) {
+		u32 freq;
+
+		cpu_mode = true;
+		/*
+		 * We're in cpu mode, convert to PCH units.
+		 *
+		 * Convert CPU pwm tick back to hz, back to new PCH units again.
+		 * this is the same formula as pch_hz_to_pwm, but the other way
+		 * around..
+		 */
+		val = pch_get_backlight(connector);
+		freq = DIV_ROUND_CLOSEST(KHz(dev_priv->rawclk_freq), val * 128);
+
+		val = lpt_hz_to_pwm(connector, freq);
+	} else
+		val = lpt_get_backlight(connector);
 	val = intel_panel_compute_brightness(connector, val);
 	panel->backlight.level = clamp(val, panel->backlight.min,
 				       panel->backlight.max);
 
-	panel->backlight.enabled = pch_ctl1 & BLM_PCH_PWM_ENABLE;
+	if (cpu_mode) {
+		u32 tmp;
+
+		/* Use PWM mode, instead of cpu clock */
+		lpt_set_backlight(connector->base.state, panel->backlight.level);
+		I915_WRITE(BLC_PWM_PCH_CTL1, pch_ctl1 | BLM_PCH_OVERRIDE_ENABLE);
+
+		tmp = I915_READ(BLC_PWM_CPU_CTL2);
+		I915_WRITE(BLC_PWM_CPU_CTL2, tmp & ~BLM_PWM_ENABLE);
+	}
 
 	return 0;
 }
-- 
2.19.1